Hemostatic disorders are characterized by uncontrolled bleeding resulting from the inability or reduced ability to form fibrin clots. Hemostatic disorders can result from a genetic defect or can be acquired as a result of an unrelated medical condition (e.g., cancer and related chemotherapy, autoimmune disease) (Kasper 2000, Hemophilia 6(Supp):13; Cohen et al. 1996, Bailiere's Clinical Hematology 9(2):331). Typically, hemostatic disorders result from the deficiency of a specific blood clotting factor. Classic examples of hemostatic disorders include hemophilia A, which results from a deficiency in factor VIII; hemophilia. B (Christmas Disease), which results from a deficiency in factor IX; and von Willebrand's disease, which results in a defect in von Willebrand's factor. Von Willebrand factor circulates in association with factor VIII and stabilizes it. It mediates the adherence of platelets to each other and to injured blood vessel walls. Other, less common hemostatic disorders include factor XI deficiency (PTA deficiency), factor XII deficiency, as well as deficiencies or structural abnormalities in fibrinogen, prothrombin, factor V, factor VII, factor X, or factor XIII (Kasper 2000, Hemophilia 6(Supp):13).
Clotting factors act in concert with one another in a coagulation cascade that ultimately results in the formation of a fibrin clot (FIG. 1). These factors can exist in a quiescent state as a proenzyme or zymogen or in an activated enzymatic state when stimulated to form a clot. Stimulation of these factors can occur by two distinct pathways, the intrinsic pathway and the extrinsic pathway. The intrinsic pathway refers to those reactions that lead to clot formation through utilization of factors present only in the plasma. In contrast, the extrinsic pathway refers to those reactions that lead to clot formation from release of membrane bound tissue factor upon vessel endothelium disruption.
Factor VII participates in both pathways cleaving factor X into the activated factor Xa in conjunction with tissue factor in the extrinsic pathway or interacting with factor IXa in the intrinsic pathway. Factor VII acts down stream and independently of factors VIII and IX when acting through the extrinsic pathway, thus bypassing the need for these clotting factors. It is, therefore, an attractive therapeutic candidate for treating hemostatic disorders, especially Hemophilia A and B. (U.S. Pat. No. 6,310,183; WO 01/58935).
Factor VII is a vitamin K-dependent plasma protein synthesized in the liver and secreted into the blood as a single-chain glycoprotein with a molecular weight of 53 kDa (Broze et al. 1980, J. Biol. Chem. 255:1242). The factor VII zymogen is converted into an activated form (FVIIa) by proteolytic cleavage at a single site, Arg152-Ile153, resulting in two chains, heavy (254 amino acids) and light (154 amino acids) linked by a single disulfide bond (Hagen et al. 1986, Proc. Natl. Acad. Sci. (USA) 83:2412). The activated form of factor VII binds to tissue factor, which then converts factor X to factor Xa. Factor Xa is required to convert prothrombin to thrombin, which converts fibrinogen to fibrin as a final stage in forming a fibrin clot.
Factor VII undergoes post-translational modifications, including vitamin K dependent carboxylation resulting in ten γ-carboxyglutamic acid residues in the N-terminal region of the molecule. Other post translational modifications include sugar moiety attachment at two naturally occurring N-linked glycosylation sites at position 145 and 322, respectively, and at two naturally occurring O-linked glycosylation sites at position 52 and 60, respectively (WO 01/58935).
Traditional therapy for hemostatic disorders calls for parenteral replacement of deficient clotting factors such as factor VII, factor VIII or factor IX (see, e.g., U.S. Pat. Nos. 6,310,183 and 4,784,950). Treatment often entails both administering clotting factors to treat acute bleeding episodes as well as administering clotting factors to prophylactically deter the occurrence of future bleeding episodes. Prophylaxis has been found to reduce the risk of developing joint problems and arthritis associated with frequent bleeding episodes (Petrini 2001, Hemophilia 7:99; Fischer et al. 2002, Blood 99(7):2337).
Traditional therapies, however, have many associated problems. Currently clotting factors must be administered parenterally in order to attain effective doses because to date non-invasive methods have not been successful in attaining therapeutic levels. Problems associated with parenteral administration include injection site occlusion, pain and infection. Use of an in-line catheter increases the risk of all of these events. Specific problems associated with the parenteral administration of clotting factors to infants and small children include central venous access. Additionally, parenteral administration of clotting factors runs the risk of precipitating a bleeding episode. These problems are particularly relevant when the patient is undergoing regular prophylactic administration of a clotting factor.
Clotting factors such as factor IX and factor VIII must be given frequently and in large doses resulting in the development of inhibitor antibodies against the clotting factor in a significant number of patients (see, e.g., Nilsson 1992, Transfusion Medicine Review 6(4):285; Cohen et al. 1996, Bailiere's Clinical Hematology 9(2):331).
One aspect of the invention provides a safer more effective treatment for hemostatic disorders. Another aspect of the invention provides for increased serum half life and increased bioavailability of therapeutics administered through non-invasive means for the treatment of hemostatic disorders thereby reducing the risk of incurring a bleeding episode, infection and injection site occlusion associated with parenteral administration. Another aspect of the invention provides therapy for hemostatic disorders with reduced risk, compared to current therapies, of developing inhibitor antibodies against the clotting factor. Yet another aspect of the invention provides for a prophylactic treatment of a hemostatic disorder.
The aspects of the invention provide for a chimeric protein comprised of at least one clotting factor and at least a portion of an immunoglobulin constant region, wherein the clotting factor is capable of promoting blood coagulation and/or fibrin clot formation.
Chimeric proteins comprising an Fc portion of an immunoglobulin are known (see, e.g., U.S. Pat. Nos. 6,030,613; 6,086,875, 6,485,726, and PCT Application No. US/02/21335) and while chimeric proteins comprised of mutant clotting factors without clotting activity, and immunoglobulins have been previously described (WO 01/02439), chimeric proteins comprising a clotting factor (i.e., having clotting activity) and at least a portion of an immunoglobulin constant region have not been described. Clotting factor as defined below and used herein refers to any molecule with clotting activity.